NEW YORK — California Gov. Jerry Brown on Monday touted steps the state has taken toward a healthier climate, but warned that powerful forces he called “climate deniers” are resisting technologies and policies designed to improve conditions.

“I like all the optimism around here, but I don’t want to minimize the steep hill that we have to climb,” Brown said at the start of a gathering of international leaders called Climate Week NYC. “Decarbonizing the economy when the economy depends so totally on carbon is not child’s play. It’s quite daunting.”

Hosted by the Climate Group, an international nonprofit organization that works with business and government to promote clean technologies and policies, the event brought together high-profile governors, along with leaders of Fortune 500 companies and multinational businesses this week to share their strategies and leadership in tackling climate change.

The discussions come amid concerns about global warming and after hurricanes Harvey and Irma caused devastating flooding in Houston and across parts of the Caribbean. Some scientists believe warmer ocean waters caused by climate change are creating stronger storms.

President Donald Trump this year announced the U.S. withdrawal from the groundbreaking Paris climate agreement.

Trump has expressed doubt about climate change and indicated that he sees the landmark international accord to reduce greenhouse gas emissions as a threat to U.S. sovereignty. The president has argued that the deal is detrimental to U.S. businesses and unfair because Washington was being made to pay more than its fair share. Trump is pushing for more “pro-America terms,” according to White House officials.

Brown said California has taken steps toward advancing climate action. In July, the governor signed legislation to extend California’s cap-and-trade program, which requires companies to buy permits to release greenhouse gas emissions, essentially giving them a financial incentive to pollute less. It is the only such initiative of its kind in the U.S. and is widely considered an international model for using threats to a company’s bottom line as an incentive to cut down on emissions. The revenue generated from the program is expected to go toward building the bullet train from Los Angeles to San Francisco.

The legislation was passed with bipartisan support — including nine Republican votes, Brown said.

“It’s the first time that I know of where Republican representatives have voted for a climate action explicitly by the name ‘climate action,’” Brown said. “That’s real crack in the armor of Republican climate denial, and I think that’s going to spread to other parts of the party.”

Brown was joined on stage at Morgan Library and Museum in Manhattan by Gov. Jay Inslee of Washington, Gov. David Ige of Hawaii, Philippe Couillard, the premier of Quebec, and Stephen Badger, chairman of the board of Mars Inc.

The chocolate giant has pledged to invest $1 billion in its “Sustainable in a Generation” plan, which aims to fight climate change by reducing greenhouse-gas emissions in its production markets by 67 percent by 2050 and tackling poverty through promoting sustainable farming.

“We’re committed,” Brown said.

At a later event Monday, the governor joined mayors and business leaders from around the world at a conference organized by C40 Cities Climate Leadership Group to emphasize the role that states, cities and regions can play in addressing climate issues.

“Cities and states can make a profound difference,” Brown said. “It would be better to have the president (on board), but the president is temporarily AWOL on this issue.”

Trump’s ideology on the climate change issue - he has questioned the science suggesting a man-made role in raising overall global temperatures and has in the past pushed a narrative that climate change is a deliberate hoax created by China - has prompted some people to be more outspoken and committed in supporting action to tackle the climate issue, Brown said.

“He is not going to be successful in the direction he’s going,” Brown said. “He’s riding a very dead horse (on) climate denial . He is accelerating the reversal through his own absurdity.”

The governor’s comments came as a new report published Monday found that the impact from the U.S. decision to withdraw from the Paris climate agreement could be significantly mitigated “thanks to the determined action demonstrated by U.S. states, cities and businesses.”

Authored by NewClimate Institute and The Climate Group, the analysis in “States, cities and businesses leading the way: a first look at decentralized climate commitments in the US” shows that the U.S. could already meet half of its climate commitments under the Paris agreement by 2025, if 22 states, 54 cities and 250 businesses headquartered in the U.S. continue to implement more than 300 obligations to reduce greenhouse emissions.

“There’s a lot of uncertainty at the federal level,” Helen Clarkson, CEO of the Climate Group, told the Times. “But what the report says is that there is plenty of action happening already. There are commitments.”

These commitments include a pledge by more than 100 businesses - including Google, Facebook and General Motors - to go to 100 percent renewable electricity, within various time frames, Clarkson said.

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Other companies have promised to bring their fleets of vehicles to 100 percent electric. Los Angeles has committed to 1,000 charging stations, the highest of any city. Britain, India and France are among several countries that have announced a phase-out of internal combustion engines by 2030/2040, Clarkson said.

Under the current scenario and if all commitments are fulfilled, greenhouse gas emissions would be reduced 12 percent to 14 percent below the 2005 level by 2025, the analysis found.

Brown this week is expected to undertake a flurry of other activities, including announcing new details regarding the September 2018 Global Climate Action Summit that is scheduled to take place in San Francisco.

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(Times staff writers Tony Barboza in Los Angeles and Chris Megerian and Russ Mitchell in San Francisco contributed to this report.)